This invention relates generally to the field of disc drive data storage devices, and more particularly, but not by way of limitation, to an apparatus and method for improving the operational performance of a disc drive by temporarily decreasing disc rotational velocity to reduce self-excited mechanical resonances during initial stages of operation before the disc drive reaches equilibrium operational temperature.
A disc drive is a data storage device used to store and retrieve computerized data in a fast and efficient manner. A typical disc drive comprises one or more rigid discs that are coated with a magnetizable medium and mounted on the hub of a spindle motor for rotation at a constant high speed. The data are stored on the discs in a plurality of concentric circular tracks by an array of transducers (xe2x80x9cheadsxe2x80x9d) mounted to a radial actuator for movement of the heads relative to the discs.
The heads are mounted via flexures at the ends of a plurality of arms which project radially outward from an actuator body. The actuator body pivots about a shaft mounted to the disc drive housing at a position closely adjacent the outer diameter of the discs. The pivot shaft is parallel with the axis of rotation of the spindle motor and the discs so that the heads move in a plane parallel with the surfaces of the discs.
Typically, the actuator employs a voice coil motor to position the heads with respect to the disc surfaces. The actuator voice coil motor includes a coil mounted on the side of the actuator body opposite the head arms so as to be immersed in the magnetic field of a magnetic circuit with one or more permanent magnets. When controlled current is passed through the coil, an electromagnetic field is set up which interacts with the magnetic field of the permanent magnets to cause the heads to move across the disc surfaces.
The heads are supported over the discs by actuator slider assemblies which include air-bearing surfaces designed to interact with a thin layer of moving air generated by the rotation of the discs, so that the heads are said to xe2x80x9cflyxe2x80x9d over the disc surfaces. Generally, the heads write data to a selected data track on the disc surface by selectively magnetizing portions of the data track through the application of a time-varying write current to the head. In order to subsequently read back the data stored on the data track, the head detects flux transitions in the magnetic fields of the data track and converts these to a read signal which is decoded by read channel circuitry of the disc drive.
Control of the position of the heads is typically achieved with a closed loop, digital servo system such as disclosed in U.S. Pat. No. 5,262,907 issued Nov. 16, 1993 to Duffy et al., assigned to the assignee of the present invention. In such a system, servo (positional control) data are interspersed with user data fields used to store the user data, with the servo data being transduced by the heads and provided to the servo system to detect head position and velocity.
During normal operation, head-disc assemblies (HDA) are subject to external and internal shocks or accelerations. A typical internal shock is one generated by the reaction to the motion of the magnetic heads and associated devices during operations. These internal shocks can cause vibrations that may shift the heads off track and cause errors that affect disc drive performance. Prior art disc drives employ servo control circuitry to detect and compensate for a shift in head position resulting from certain shocks. Unfortunately the servo circuitry is only capable of countering the effect of certain accelerations that are not too large.
One area that is difficult for prior art methods to correct involves the self-excitation of mechanical resonances with in the disc drive, which are primarily established by rotation of the spindle motor. This non-linear vibration problem is known as a self-excited vibration or a xe2x80x9cchirp.xe2x80x9d A xe2x80x9cchirpxe2x80x9d is basically a resonance condition in which the excitation level increases with the magnitude of the resonance. This interaction causes a non-linear, highly unstable condition in which the disc drive mechanics vibrate enough to create a non-functional disc drive. It has been found that these resonances are related to the mechanical configuration of the drive, as well as the input vibratory spectrum caused by rotation of the bearings in the spindle. As higher levels of performance are achieved, this problem worsens since higher performances are achieved by increasing the number of discs, rotating the discs at higher rotational speeds and utilizing higher track densities.
Two detrimental effects come from self excited vibrations. First, a disc experiences undesired acoustic noise as resonances are transmitted to the disc drive housing. Secondly, there is an undesired performance degradation as the vibrations cause the heads and discs to vibrate, making positional control during seeking or track following difficult, if not temporarily impossible. Normally a design change can move the resonant frequency away from the excitation frequency, but since some resonant frequencies are temperature dependent, there can still be a problem whenever there is a temperature change. This most often occurs as the disc drive heats up during initial start-up procedures.
It is this need for an improved approach to reducing the effects of self-excited resonances in the drive that the present invention is directed.
The present invention is directed to an apparatus and method for improving the operational performance of a disc drive by reducing effects of self-excited mechanical resonances established within the disc drive.
As exemplified by preferred embodiments, a disc drive is provided with a spindle motor which supports a disc with a disc recording surface. Data are stored to and retrieved from the disc recording surface by a read/write head which is controllably positionable adjacent the surface. A spindle motor control circuit applies current to the spindle motor to rotate the disc at a desired rotational velocity. A disc drive processor provides top level control of the disc drive, and a temperature sensor provides the processor with an indication of the operational temperature of the drive.
Upon disc drive initialization, the processor instructs the spindle motor control circuit to accelerate the disc from rest to a nominal operational rotational velocity. Normal disc drive operations are thereafter carried out as the operational temperature of the disc drive transitions from an initial, ambient temperature to an equilibrium temperature associated with steady-state operation over an extended period of time.
Before the temperature of the disc drive reaches the equilibrium temperature, when a self-excited mechanical resonance is detected within the disc drive, the processor instructs the spindle motor control circuit to decrease the rotational velocity of the disc to a reduced operational rotational velocity less than the nominal operational rotational velocity. The reduced operational rotational velocity is applied to reduce the effects of the self-excited mechanical resonance by modifying the excitation frequency spectrum input to remaining portions of the disc drive by the spindle motor. After temporarily operating at the reduced velocity, the processor thereafter instructs the spindle motor control circuitry to restore the rotational velocity of the disc to the nominal operational rotational velocity.
Preferably, the mechanical configuration of the disc drive is selected so that the effects of the self-excited mechanical resonance are greater at temperatures less than the equilibrium temperature as compared to when the disc drive is operated at the equilibrium temperature. In this way, temperature dependent mechanical interactions have larger effects upon the disc drive at temperatures below equilibrium temperature and are significantly reduced once the disc drive has completed the warming cycle.
As desired, the processor continues to operate the disc drive at the reduced rotational velocity, or to sequentially switch between the reduced rotational velocity and the nominal operational rotational velocity until the disc drive reaches the equilibrium temperature.
These and various other features as well as advantages which characterize the present invention will be apparent from a reading of the following detailed description and a review of the associated drawings.